Utility Plant, Palo Verde and Other Jointly-Owned Utility Plant

The table below presents the balance of each major class of depreciable assets at December 31, 2017 (in thousands):



	Gross Plant		Accumulated Depreciation			Net Plant
Nuclear production	$	994,075	$	(338,699	)	$	655,376
Steam and other	952,672		(214,551		)	738,121
Total production	1,946,747		(553,250		)	1,393,497
Transmission	520,126		(264,480		)	255,646
Distribution	1,183,289		(374,438		)	808,851
General	226,325		(66,347		)	159,978
Intangible	105,608		(61,660		)	43,948
Total	$	3,982,095	$	(1,320,175	)	$	2,661,920

The Company owns a 15.8% interest in each of the three nuclear generating units and common facilities at Palo Verde, in Wintersburg, Arizona. The Palo Verde Participants include the Company and six other utilities: APS, Southern California Edison Company ("SCE"), PNM, Southern California Public Power Authority, Salt River Project Agricultural Improvement and Power District ("SRP") and the Los Angeles Department of Water and Power.

A summary of the Company’s investment in jointly-owned utility plant, excluding fuel inventories, at December 31, 2017 and 2016 is as follows (in thousands):



	December 31, 2017						December 31, 2016
	Palo Verde			Other (a)			Palo Verde			Other (a)
Electric plant in service	$	994,075		$	97,603		$	948,382		$	97,652
Accumulated depreciation	(338,699		)	(72,822		)	(320,000		)	(74,408		)
Construction work in progress	40,946			1,014			50,598			1,895
Total	$	696,322		$	25,795		$	678,980		$	25,139

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(a) Includes three jointly-owned transmission lines.

Amortization of intangible plant (software) is provided on a straight-line basis over the estimated useful life of the asset (ranging from 3 to 15 years). The table below presents the actual and estimated amortization expense for intangible plant for the previous three years and for the next five years (in thousands):



2015	$	6,482
2016	5,302
2017	6,409
2018 (estimated)	6,835
2019 (estimated)	6,485
2020 (estimated)	6,048
2021 (estimated)	5,128
2022 (estimated)	4,328

Palo Verde

The operation of Palo Verde and the relationship among the Palo Verde Participants is governed by the Arizona Nuclear Power Project Participation Agreement (the "ANPP Participation Agreement"). APS serves as operating agent for Palo Verde, and under the ANPP Participation Agreement, the Company has limited ability to influence operations and costs at Palo Verde. Pursuant to the ANPP Participation Agreement, the Palo Verde Participants share costs and generating entitlements in the same proportion as their percentage interests in the generating units, and each participant is required to fund its share of fuel, other operations, maintenance and capital costs. The Company’s share of direct expenses in Palo Verde and other jointly-owned utility plants is reflected in fuel expense, other operations expense, maintenance expense, miscellaneous other deductions, and taxes other than income taxes in the Company’s statements of operations. The ANPP Participation Agreement provides that if a participant fails to meet its payment obligations, each non-defaulting participant shall pay its proportionate share of the payments owed by the defaulting participant. Because it is impracticable to predict defaulting participants, the Company cannot estimate the maximum potential amount of future payment, if any, which could be required under this provision.

Nuclear Regulatory Commission. The Nuclear Regulatory Commission ("NRC") regulates the operation of all commercial nuclear power reactors in the United States, including Palo Verde. The NRC periodically conducts inspections of nuclear facilities and monitors performance indicators to enable the agency to arrive at objective conclusions about a licensee’s safety performance.

Palo Verde Operating Licenses. Operation of each of the three Palo Verde Units requires an operating license from the NRC. The NRC issued full power operating licenses for Unit 1 in June 1985, Unit 2 in April 1986 and Unit 3 in November 1987 and issued renewed operating licenses for each of the three units in April 2011, which extended the licenses for Units 1, 2 and 3 to June 2045, April 2046 and November 2047, respectively.

Decommissioning. Pursuant to the ANPP Participation Agreement and federal law, the Company funds its share of the estimated costs to decommission Palo Verde Units 1, 2 and 3, including the Common Facilities, through the term of their respective operating licenses and is required to maintain a minimum accumulation and funding level in its decommissioning account at the end of each annual reporting period during the life of the plant. The Company has established external trusts with an independent trustee, which enables the Company to record a current deduction for federal income tax purposes for most of the amounts funded. At December 31, 2017, the Company’s decommissioning trust fund had a balance of $286.9 million, which is above its minimum funding level. The Company monitors the status of its decommissioning funds and adjusts deposits, if necessary.

Decommissioning costs are estimated every three years based upon engineering cost studies performed by outside engineers retained by APS. In April 2017, the Palo Verde Participants approved the 2016 Palo Verde decommissioning study (“2016 Study”). The 2016 Study estimated that the Company must fund approximately $432.8 million (stated in 2016 dollars) to cover its share of decommissioning costs which was an increase in decommissioning costs of $52.1 million (stated in 2016 dollars) from the 2013 Palo Verde decommissioning study. The effect of this change increased the ARO by $3.5 million, which was recorded during the second quarter of 2017, and increased annual expenses starting in April 2017. Although the 2016 Study was based on the latest available information, there can be no assurance that decommissioning cost estimates will not increase in the future or that regulatory requirements will not change. In addition, until a new low-level radioactive waste repository opens and operates for a number of years, estimates of the cost to dispose of low-level radioactive waste are subject to uncertainty. As provided in the ANPP Participation Agreement, the participants are required to conduct a new decommissioning study every three years. While the Company attempts to seek amounts in rates to meet its decommissioning obligations, it is not able to conclude given the evidence available to it now that it is probable these costs will continue to be collected over the period until decommissioning begins in 2044. The Company is ultimately responsible for these costs and its future actions combined with future decisions from regulators will determine how successful the Company is in this effort.

Spent Fuel and Waste Disposal. Pursuant to the Nuclear Waste Policy Act of 1982, as amended in 1987 (the "NWPA"), the DOE is legally obligated to accept and dispose of all spent nuclear fuel and other high-level radioactive waste generated by all domestic power reactors by 1998. The DOE's obligations are reflected in a contract for Disposal of Spent Nuclear Fuel and/or High-Level Radioactive Waste (the "Standard Contract") with each nuclear power plant. The DOE failed to begin accepting spent nuclear fuel by 1998. On December 19, 2012, APS, acting on behalf of itself and the Palo Verde Participants, filed a second breach of contract lawsuit against the DOE. This lawsuit sought to recover damages incurred due to the DOE’s failure to accept Palo Verde’s spent nuclear fuel for the period beginning January 1, 2007 through June 30, 2011. On August 18, 2014, APS and the DOE entered into a settlement agreement stipulating to a dismissal of the lawsuit. Pursuant to the terms of the August 18, 2014 settlement agreement, APS files annual claims for the period July 1 of the then-previous year to June 30 of the then-current year. The settlement agreement, as amended, provides APS with a method for submitting claims and receiving recovery for costs incurred through December 31, 2016, which has been extended to December 31, 2019. The Company's share of costs recovered are presented below (in thousands):



			Amount Credited
			to Customers
			through Fuel		Period Credited
Costs Recovery Period	Amount Refunded		Adjustment Clauses		to Customers

January 2007 - June 2011	$	9,076	$	7,944	September 2014
July 2011 - June 2014	6,643		5,759		March 2015
July 2014 - June 2015	1,884		1,581		March 2016
July 2015 - June 2016	1,779		1,432		March 2017

On October 31, 2017, APS filed an $8.9 million claim for the period July 1, 2016 through June 30, 2017. The Company's share of this claim is approximately $1.4 million. In February 2018, the DOE approved this claim. Any reimbursement is anticipated to be received in the first half of 2018, and the majority of the reimbursement received by the Company is expected to be credited to customers through the applicable fuel adjustment clauses.

DOE’s Construction Authorization Application for Yucca Mountain. The DOE had planned to meet its disposal obligations by designing, licensing, constructing and operating a permanent geologic repository in Yucca Mountain, Nevada. In March 2010, the DOE filed a motion to dismiss with prejudice its Yucca Mountain construction authorization application that was pending before the NRC. Several interested parties have intervened in the NRC proceeding. The Company cannot predict when spent fuel shipments to the DOE will commence.

Palo Verde has sufficient capacity at its on-site independent spent fuel storage installation (“ISFSI”) to store all of the nuclear fuel that will be irradiated during the initial operating license period, which ends in December 2027. Additionally, Palo Verde has sufficient capacity at its on-site ISFSI to store a portion of the fuel that will be irradiated during the period of extended operation, which ends in November 2047. If uncertainties regarding the United States government’s obligation to accept and store spent fuel are not favorably resolved, APS will evaluate alternative storage solutions that may obviate the need to expand the ISFSI to accommodate all of the fuel that will be irradiated during the period of extended operation.

Liability and Insurance Matters. The Palo Verde Participants have insurance for public liability resulting from nuclear energy hazards to the full limit of liability under federal law, which is currently at $13.4 billion. This potential liability is covered by primary liability insurance provided by commercial insurance carriers in the amount of $450.0 million, and the balance is covered by an industry-wide retrospective assessment program. If a loss at a nuclear power plant covered by the programs exceeds the accumulated funds in the primary level of protection, the Company could be assessed retrospective premium adjustments on a per incident basis. Under federal law, the maximum assessment per reactor under the program for each nuclear incident is approximately $127.3 million, subject to an annual limit of $19.0 million. Based upon the Company's 15.8% interest in the three Palo Verde units, the Company's maximum potential assessment per incident for all three units is approximately $60.4 million, with an annual payment limitation of approximately $9.0 million.

The Palo Verde Participants maintain $2.75 billion of "all risk" nuclear property insurance. The insurance provides coverage for property damage and decontamination at Palo Verde. For covered incidents involving property damage not accompanied by a release of radioactive material, the policy's coverage limit is $2.25 billion. The Company has also secured insurance against portions of any increased cost of generation or purchased power and business interruption resulting from a sudden and unforeseen outage of any of the three units. The insurance coverage discussed in this and the previous paragraph is subject to certain policy conditions and exclusions. A mutual insurance company whose members are utilities with nuclear facilities issues these policies. If losses at any nuclear facility covered by this mutual insurance company were to exceed the accumulated funds for these insurance programs, the Company could be assessed retrospective premium adjustments of up to $13.0 million for the current policy period.

Palo Verde Operations and Maintenance Expense. Included in other operations and maintenance expenses are expenses associated with Palo Verde as follows (in thousands):



Years Ended December 31,
2017		2016		2015
$	99,364	$	96,914	$	97,639

Four Corners

On July 6, 2016, the Company sold its interests in Four Corners for $32.0 million to 4C Acquisition, LLC, an affiliate of APS ("APS's affiliate"), and Pinnacle West Capital Corporation ("Pinnacle West"), the parent company of APS and APS's affiliate. No significant gain or loss was recorded for this sale. APS's affiliate assumed responsibility for all Four Corners capital expenditures made after July 6, 2016, which assumption is guaranteed by Pinnacle West. In addition, APS's affiliate will indemnify the Company against certain liabilities and costs related to the future operation of Four Corners, which indemnification is guaranteed by Pinnacle West. See Part II, Item 8, Financial Statements and Supplementary Data, Note C for a discussion of regulatory filings associated with Four Corners.